The intravenous pharmacokinetics of butorphanol and detomidine dosed in combination compared with individual dose administrations to exercised horses.

In equine and racing practice, detomidine and butorphanol are commonly used in combination for their sedative properties. The aim of the study was to produce detection times to better inform European veterinary surgeons, so that both drugs can be used appropriately under regulatory rules. Three independent groups of 7, 8 and 6 horses, respectively, were given either a single intravenous administration of butorphanol (100 µg/kg), a single intravenous administration of detomidine (10 µg/kg) or a combination of both at 25 (butorphanol) and 10 (detomidine) µg/kg. Plasma and urine concentrations of butorphanol, detomidine and 3-hydroxydetomidine at predetermined time points were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The intravenous pharmacokinetics of butorphanol dosed individually compared with co-administration with detomidine had approximately a twofold larger clearance (646 ± 137 vs. 380 ± 86 ml hr-1  kg-1 ) but similar terminal half-life (5.21 ± 1.56 vs. 5.43 ± 0.44 hr). Pseudo-steady-state urine to plasma butorphanol concentration ratios were 730 and 560, respectively. The intravenous pharmacokinetics of detomidine dosed as a single administration compared with co-administration with butorphanol had similar clearance (3,278 ± 1,412 vs. 2,519 ± 630 ml hr-1  kg-1 ) but a slightly shorter terminal half-life (0.57 ± 0.06 vs. 0.70 ± 0.11 hr). Pseudo-steady-state urine to plasma detomidine concentration ratios are 4 and 8, respectively. The 3-hydroxy metabolite of detomidine was detected for at least 35 hr in urine from both the single and co-administrations. Detection times of 72 and 48 hr are recommended for the control of butorphanol and detomidine, respectively, in horseracing and equestrian competitions.

Pharmacokinetics and pharmacodynamics of butorphanol following intravenous administration to the horse.

Butorphanol is a narcotic analgesic commonly used in horses. Currently, any detectable concentration of butorphanol in biological samples collected from performance horses is considered a violation. The primary goal of the study reported here was to update the pharmacokinetics of butorphanol following intravenous administration, utilizing a highly sensitive liquid chromatography-mass spectrometry (LC-MS) assay that is currently employed in many drug-testing laboratories. An additional objective was to characterize behavioral and cardiac effects following administration of butorphanol. Ten exercised adult horses received a single intravenous dose of 0.1 mg/kg butorphanol. Blood and urine samples were collected at time 0 and at various times for up to 120 h and analyzed using LC-MS. Mean±SD systemic clearance, steady-state volume of distribution, and terminal elimination half-life were 11.5±2.5 mL/min/kg, 1.4±0.3 L/kg, and 5.9±1.5 h, respectively. Butorphanol plasma concentrations were below the limit of detection (LOD) (0.01 ng/mL) by 48 h post administration. Urine butorphanol concentrations were below the LOD (0.05 ng/mL) of the assay in seven of 10 horses by 120 h post drug administration. Following administration, horses appeared excited as noted by an increase in heart rate and locomotion. Gastrointestinal sounds were markedly decreased for up to 24 h.

[Chemical-toxicological analysis of butorphanol].

The conditions of butorphanol isolation from biological fluids were studied. The method of its extraction with the mix of organic solvents by pH 12 was proposed. How to identify butorphanol with the methods of thin-layer chromatography, ultraviolet spectrometry, high-performance liquid chromatography, gas chromatography with a detector of electron capture, chromato-mass spectrometry was developed. Possibility of use ultraviolet spectrometry for quantitative assessment of butorphanol was shown.

The pharmacokinetics of butorphanol and its metabolites at steady state following nasal administration in humans.

The single-dose and steady state pharmacokinetics of butorphanol and its metabolites, hydroxybutorphanol (HO-B) and norbutorphanol (NOR-B), were studied in nine healthy male volunteers. Each subject received a single 1 mg dose of butorphanol on days 1 and 6, and a 1 mg dose every 6 h (q6h) on days 2-5, via nasal administration. Serial blood and urine samples were collected for 24 h after the first dose on day 1 and for 72 h at steady state on day 6. Plasma and urine samples were analyzed for free and conjugated butorphanol, HO-B, and NOR-B. The plasma samples were analyzed using validated gas chromatography-electron capture negative chemical ionization-mass spectrometric methods and the urine samples were analyzed using a validated HPLC procedure. In the plasma, conjugated metabolites were not detected and only trace amounts of NOR-B were present. Therefore, pharmacokinetic parameters could not be estimated for NOR-B and conjugated metabolites. AUC0-->infinity of butorphanol after the first dose and AUC0-->tau at steady state were not statistically different, indicating that the kinetics of butorphanol were not significantly altered after repeated dosing. Steady state levels of butorphanol were attained within 3 days (d) of q6h dosing and the accumulation index was 1.2 for butorphanol. Due to a relatively long t1/2 of 15 h of HO-B compared to the dosing interval (q6h), the accumulation index was 6.0 for this metabolite. The evaluation of the molar plasma concentration ratio of HO-B to butorphanol as a function of time revealed that HO-B exhibits elimination-rate-limited kinetics. Similarly to butorphanol, steady state levels of HO-B were attained within 3 d of q6h dosing.

Determination of butorphanol in horse race urine by immunoassay and gas chromatography-mass spectrometry.

An analytical procedure to screen butorphanol in horse race urine using ELISA kits and its confirmation by GC-MS is described. Urine samples (5 ml) were subjected to enzymatic hydrolysis and extracted by solid-phase extraction. The residues were then evaporated, derivatized and injected into the GC-MS system. The ELISA test (20 microl of sample) was able to detect butorphanol up to 104 h after the intramuscular administration of 8 mg of Torbugesic, and the GC-MS method detected the drug up to 24 h in FULL SCAN or 31 h in the SIM mode. Validation of the GC-MS method in the SIM mode using nalbuphine as internal standard included linearity studies (10-250 ng/ml), recovery (+/-100%), intra-assay (4.1-14.9%) and inter-assay (9.3-45.1%) precision, stability (10 days), limit of detection (10 ng/ml) and limit of quantitation (20 ng/ml).

Lack of pharmacokinetic interaction between butorphanol nasal spray and cimetidine.

The potential for a pharmacokinetic interaction between butorphanol nasal spray and cimetidine, under steady state conditions, was evaluated in 16 healthy male volunteers. Subjects received either a 1 mg butorphanol nasal spray every 6 h or a 300 mg cimetidine tablet every 6 h on days 1 4, the combination of two compounds every 6 h on days 5-8 and the original treatment as described in the first segment (days 1-4) on days 9-12. Serial blood and urine samples were collected on days 4, 8 and 12, and additional blood samples were taken immediately, prior to the morning dose on days 3, 7 and 11. Based on the analysis of the Cmin samples, the plasma concentrations of cimetidine and butorphanol achieved steady state by the third day of dosing. No statistically significant differences were found in the plasma concentrations of butorphanol or cimetidine (except for t1/2 and MRT) between any of the treatment phases. Butorphanol nasal spray and cimetidine can be co-administered without any adjustment of dosage for either drug.

High-performance liquid chromatographic method for the quantitative determination of butorphanol, hydroxybutorphanol, and norbutorphanol in human urine using fluorescence detection.

A sensitive, quantitative reversed-phase high-performance liquid chromatographic method has been established for the simultaneous determination of butorphanol, a synthetic opioid, and its metabolites, hydroxybutorphanol and norbutorphanol, in human urine samples. The method involved extraction of butorphanol, hydroxybutorphanol, and norbutorphanol from urine (1.0 ml), buffered with 0.1 ml of 1.0 M ammonium acetate (pH 6.0), onto 1-ml Cyano Bond Elut columns. The eluent was evaporated under nitrogen and low heat, and reconstituted with the HPLC mobile phase, acetonitrile-methanol-water (20:10:70, v/v/v), containing 10 mM ammonium acetate and 10 mM TMAH (pH 5.0). The samples were chromatographed on a reversed-phase octyl 5-microns column. The analysis was accomplished by detection of the fluorescence of the three analytes, at excitation and emission wavelengths of 200 nm and 325 nm, respectively. The retention times for hydroxybutorphanol, norbutorphanol, the internal standard, and butorphanol were 5.5, 9.0, 13.0, and 23.4 min respectively. The validated quantitation range of the method was 1-100 ng/ml for butorphanol and hydroxybutorphanol, and 2-200 ng/ml for norbutorphanol in urine. The observed recoveries for butorphanol, hydroxybutorphanol, and norbutorphanol were 93%, 72%, and 50%, respectively. Standard curve correlation coefficients of 0.995 or greater were obtained during validation experiments and analysis of study samples. The method was applied on study samples from a clinical study of butorphanol, providing a pharmacokinetic profiling of butorphanol.

Determination of drugs in biological samples by thin-layer chromatography-tandem mass spectrometry.

In this work thin-layer chromatography-tandem mass spectrometry (TLC-MS-MS) allowed detection and confirmation of caffeine and nicotine in human urine and of butorphanol, betamethasone, and clenbuterol in equine urine. In most cases of trace analysis of labile compounds the drugs could not be identified unless they were developed on a TLC plate, scraped from the plate and the TLC scrape eluted with a suitable organic solvent prior to MS-MS. Usually a sample prepared in this way still had several components in it, but was sufficiently cleaned up to allow collision-induced dissociation (CID) experiments to unequivocally identify the drug. In contrast, trace levels of labile drugs could not be identified by CID experiments either directly from the raw urine extracts or by thermally desorbing them from the TLC scrape.

Furosemide, Patella vulgata beta-glucuronidase and drug analysis: conditions for enhancement of the TLC detection of apomorphine, butorphanol, hydromorphone, nalbuphine, oxymorphone and pentazocine in equine urine.

We have investigated the action of five sources of beta-glucuronidase enzymes on the hydrolysis of glucuronides of apomorphine, butorphanol, hydromorphone, nalbuphine, oxymorphone and pentazocine in equine urine. For all glucuronides tested, Patella vulgata beta-glucuronidase yielded the largest thin layer chromatographic (TLC) spots. For oxymorphone, P. vulgata was the only treatment to yield detectable TLC spots under test parameters. For these six drugs, TLC spot size and chromatographic quality were compared between control horses and horses pretreated with furosemide four hours earlier. Furosemide pretreatment produced a statistically significant increase in spot size and was found to enhance chromatogram quality. These findings support previous suggestions that P. vulgata is a superior drug-glucuronide hydrolyzing enzyme. They also support earlier reports that administration of furosemide at four hours pre-race is unlikely to result in significant interference with routine drug testing procedures.

Disposition of parenteral butorphanol in man.

The metabolism and elimination of 3H-butorphanol (levo-3, 14-dihydroxy-N-(cyclobutylmethyl)[15-3H]morhinan) tartrate were determined in man after therapeutic im (2 mg) and iv (1 mg) doses. As judged from urinary excretion of radioactivity, the im dose was completely absorbed. Butorphanol was rapidly distributed to tissues, had a plasma half-life of about 3 hr, and was extensively metabolized prior to elimination. The major route of elimination was renal, with fecal excretion being a minor route. Hydroxybutorphanol [3, 14-dihydroxy-N-(trans-3'-hydroxycyclobutylmethyl)morphinan] was isolated and identified as a major urinary metabolite and was also present in the plasma. The disposition of butorphanol is compared and contrasted to the disposition of morphine and pentazocine.